1. Field of the Invention
The present invention relates generally to flow rate controllers for controlling the liquid flow in a sewerage system or the like. More particularly, the invention relates to flow rate controllers of the type where the liquid flow to be controlled is braked by being set in rotary motion in a vortex or braking chamber.
2. The Prior Art
In, for example, a combined sewerage system where waste water and storm water are collected in common sewers, one wishes to avoid dimensioning the system according to the peak loads that may occur, for which reason use is usually made of some type of control to restrict the amount of liquid per unit of time discharged to the pipe system. If the pipe system is overloaded, and if there are no facilities for controlling the liquid flow to the system, a heavy rain for example may cause, in the waste water pipes connected to the pipe system, a back pressure from the cellars of residential buildings and cause flooding of the cellars. Such flow control ay be desirable also in separate sewerage systems.
It is already known, for flow control purposes, to utilise retardation stores, throttling pipes or level-controlled throttle valves. If, for example, the flow is controlled by means of a disk which is mounted in the pipe and has a small aperture through which the liquid is caused to pass, there is obtained through said aperture a liquid flow Q according to the formula EQU Q=.mu.A.sqroot.2 g H (1)
in which A is the cross-sectional area of the aperture, H is the pressure head with respect to the centre of the aperture, g is the gravitational acceleration, and .mu. is a discharge coefficient which is about 0.6 for a sharp-edged aperture. A diagram shown in FIG. 1 illustrates by means of a curve K1 how the discharged liquid flow Q increases along a parabola when the liquid is dammed up in front of the apertured disk, i.e. when the pressure head H increases. The discharge curve K1 is here said to be unbraked.
In many cases, it is desired to be able, for a given pressure head H, to reduce the liquid flow Q without changing the throughflow area A because, if A is small, the risk of blocking the controller increases and may interfere with the proper functioning.
This desideratum is partly satisfied by the type of flow controller which is described in, for example, DK-C-135,904, DK-A-5120/79 and PCT application No. 84 902 583.8. These prior art flow controllers which are intended to be mounted for example at or in the outlet duct of a gully for limiting the amount of liquid discharged per unit of time from the gully to a sewerage system, comprises a braking chamber which is symmetrical with respect to rotation and has a central outlet aperture. Flow control is achieved by conducting the liquid tangentially into the braking chamber at the periphery thereof perpendicular to the outlet direction, whereby the liquid is set in rotary motion in the braking chamber and then leaves the controller through the outlet aperture. In this manner, the major part of the pressure energy of the liquid is converted into rotational energy, i.e. the liquid flow is braked and the discharged amount of liquid per unit of time Q is reduced. With these prior art flow controllers, it is possible, with the same free aperture A as in the above-mentioned case where the aperture has a sharp edge, to reduce the .mu.-value considerably, as illustrated in FIG. 1 by the curve K2 which here is said to be braked.
It thus is the object of these prior art vortex brake type flow controllers to achieve a relatively large throughflow area in the controller so that the controller becomes reliable in operation and is not blocked by impurities in the liquid, and thereby to establish a large hydraulic resistance, i.e. a low .mu.-value.
Nevertheless, the vortex brake type flow controllers described above suffer from several disadvantages. In the first place, the braking effect, and thus the capacity of said flow controllers, is limited by the physical size of the controller, which frequently causes difficulties in the mounting of the controller in the relatively narrow spaces of sewerage systems. It therefore is desired to be able to increase the braking effect while retaining the size of the controller.
A second disadvantage of the known vortex brake type flow controllers is that, in order to cover all the requirements of the market, one is compelled to stock an extensive range of controllers in different sizes because a controller of a given size is optimal only for a given Q-value and a given H-value.
It therefore is desirable to be able to control very small and, at the same time, highly varying amounts of liquid per unit of time with varying pressure heads with as few controller sizes as possible.